Control of arbitrary scan path of a rotating magnetron

ABSTRACT

A control system and method for controlling two motors determining the azimuthal and circumferential position of a magnetron rotating about the central axis of the sputter chamber in back of its target sputtering and capable of a nearly arbitrary scan path, e.g., with a planetary gear mechanism. A system controller periodically sends commands to the motion controller which closely controls the motors. Each command includes a command ticket, which may be one of several values. The motion controller accepts only commands having a command ticket of a different value from the immediately preceding command. One command selects a scan profile stored in the motion controller, which calculates motor signals from the selected profile. Another command instructs a dynamic homing command which interrogates sensors of the position of two rotating arms to determine if the arms in the expected positions. If not, the arms are rehomed.

FIELD OF THE INVENTION

The invention relates generally to sputtering of materials. Inparticular, the invention relates to the control of the scan path of amagnetron in back of a plasma sputtering target.

BACKGROUND ART

Sputtering, alternatively called physical vapor deposition (PVD), is themost prevalent method of depositing layers of metals and relatedmaterials in the fabrication of semiconductor integrated circuits. Thecommercially most important form of sputtering is plasma sputteringusing a magnetron in back of the sputtering target to increase thedensity of the plasma and increase the sputtering rate. A typicalmagnetron includes a magnetic pole of one magnetic polarity surroundinganother magnetic pole of the opposed magnetic polarity. A gap of nearlyconstant width and forming a closed loop separates the two poles andsets up a closed plasma track adjacent the sputtering face of thetarget.

Magnetron sputtering was originally used to deposit nearly planar andrelatively thick layers of a metal such as aluminum, which wasthereafter etched into a pattern of horizontal interconnect. A typicalmagnetron used for this type of sputtering has a relatively large kidneyshape with the closely adjacent poles positioned near the periphery ofthe pattern. The magnetron extends from about the center of the targetto near its usable periphery and is rotated about the target center toproduce uniform sputtering of the target and hence sputter deposition onthe wafer. The large size of the magnetron can produce fairly uniformtarget erosion and uniform thickness of the sputtered layer deposited onthe wafer.

More recently, however, magnetron sputtering has been extended todeposit thin, nearly conformal layers into high aspect-ratio holesformed in dielectric layers, such as vias for vertical interconnects ortrenches for capacitive memories. Examples of such sputtered layersinclude a barrier layer of, for example, tantalum and tantalum nitride,to prevent migration of metal into the underlying dielectric and acopper seed layer to act as plating electrode and nucleation layer forcopper later filled into the via hole by electrochemical plating (ECP).Sputtering into such deep and narrow holes relies in part on a largefraction of ionized sputtered atoms produced in a high plasma density,which can be achieved by a small magnetron which concentrates the targetpower to a small area of the target, thus producing a high powerdensity. It has been found that small magnetrons scanned near theperiphery of the target effectively can nonetheless produce a nearlyuniform sputter deposition because the sputtered ions diffuse toward thecenter of the wafer as they travel from the target to the wafer.

However, it is sometimes desired to sputter a wider band on the targetwith a smaller magnetron. Miller et al. describe a planetary magnetron(PMR) in U.S. Pat. No. 6,852,202, incorporated herein by reference. Inthe PMR sputter chamber, an inner arm is rotated about the target centerand an outer arm spins about an pivot axis at an end of the inner armand has a magnetron mounted on its end offset from the pivot axis. Thedescribed PMR mechanism includes a planetary gear mechanism with a sungear fixed at the target center and coupled to a gear rotating on thepivot axis and supporting the second arm. The planetary gear mechanismproduces a multi-lobed scan pattern in which the radial extent of thescan pattern and the number of lobes is established by the lengths ofthe two arms and the gear ratio of the gear mechanism. Although thisscan pattern has been quite effective in advanced sputteringapplications, the lobed scan pattern may not be the optimal one and itis desired to change the scan pattern without changing physical parts ofthe scan mechanism.

SUMMARY OF THE INVENTION

A system and method control two motors causing the movement of anmagnetron along a nearly arbitrary path on the back of a sputteringtarget. A system controller periodically sends command to a motioncontroller which interprets those commands and accordingly drives thetwo motors.

According to one aspect of the invention, each command includes acommand ticket which can assume one of several acceptable values as wellas possible a no-operation value. The system controller may resendcommands with the same value of the command ticket but changes the valuefor a new command. The motion controller does not change its control ofthe motors upon receipt of a command unless that command includes acommand ticket with an acceptable value other than that of thepreviously received command.

According to another aspect of the invention, plural scanning profilesof a magnetron scanning path are stored in the motion controller. Onecommand is a profile command selecting one of the stored profiles. Uponreceipt of the profile command, the motion controller controls themotors to execute the selected profile.

According to yet another aspect of the invention, the system includestwo sensors which can detect when respective arms or other members ofthe scan mechanism pass nearby. One command is a dynamic homing command.Upon receipt of the dynamic homing command, the motion controller causesthe arms to move along preselected paths and determines if the sensorsdetect the arms at the expected times. If not, the control systemrehomes the scan mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a sputter chamberincluding an embodiment of the motor control system for an epicyclicmagnetron scanning mechanism.

FIG. 2 is an orthographic view of a universal magnetron scanningmechanism.

FIG. 3 is a cross-sectional view of part of the magnetron scanningmechanism of FIG. 2.

FIG. 4 is a plan view of reservoir top wall on which the magnetronscanning mechanism is mounted and providing mounting holes for opticalsensors associated with it.

FIG. 5 is diagram of an embodiment of a motor control circuit accordingto the invention.

FIG. 6 is a plan view of a complex profile for a magnetron scanningpattern.

FIG. 7 is a graph illustrating the angle and radius of the magnetronfollowing the profile of FIG. 6.

FIG. 8 is a schematic plan view of a model of the scanning mechanismused to explain the operation of some of the commands.

FIG. 9 is a flow diagram of one method of operating the scanningmechanism with one command protocol consistent with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Miller et al. (hereafter Miller) describe a two-shaft epicyclicmagnetron scan mechanism in U.S. patent application Ser. No. 11/924,573,filed Oct. 25, 2007 and incorporated herein by reference, particularlyfor the detailed mechanism and scan patterns available. According toMilller, a sputter chamber 10 schematically illustrated in thecross-sectional view of FIG. 1 includes a conventional main chamber 12generally symmetric around a central axis 14 and supporting a targetassembly 18 through an adapter 20 and an isolator 22. The targetassembly 18 may be formed from the material to be sputtered or mayinclude a target tile facing the interior of the chamber body 12 andbonded to a backing plate extending laterally over the isolator 22. Thesputter chamber 10 also includes an epicyclic scan actuator 26 locatedin the back of the target assembly 18 and including an inner rotaryshaft 28 and a tubular outer rotary shaft 30, which are coaxial and arearranged about and extend along the central axis 14 and can rotate aboutit. A first motor 32 is coupled to the inner rotary shaft 28 by a drivegear 34 or other mechanical means such as a belt wrapped around twopulleys to rotate it. A second motor 36 is similarly coupled to theouter rotary shaft 30 through another drive gear 38 or mechanical meansto rotate it independently of the rotation of the inner rotary shaft.28.The shafts 28, 30 are coupled to an epicyclic mechanism 40, whichsupports a magnetron 42 through a mount 44 and scans it over the back ofthe target assembly 18 in a nearly arbitrary pattern determined by therotations of the rotary shafts 28, 30. The principal embodiment of theMiller epicyclic mechanism 40 is a planetary gear system which differsfrom the PMR mechanism by a sun gear which is rotated by the innerrotary shaft 28 rather than being fixed, as is described in more detailby Miller and will be described in lesser detail below. The magnetron 42typically includes a magnetic yoke 46 supporting and magneticallycoupling an inner pole 48 of one magnetic polarity along the centralaxis 14 and an outer pole 50 of the opposed magnetic polarity andsurrounding the inner pole 48. The magnetron 42 and large portions ofthe epicyclic mechanism 40 are disposed in an unillustrated coolingreservoir of recirculating chilled sealed to the back of the target orits backing plate in order to maintain the target assembly 18 at areasonably low temperature.

Returning to the main chamber 12, a vacuum pump 60 pumps the interior ofthe main chamber 12 through a pumping port 62. A gas source 64 suppliesa sputter working gas, such as argon, into the chamber 12 through a massflow controller 66. If reactive sputtering is desired, for example, of ametal nitride, a reactive gas, such as nitrogen in the example, is alsosupplied.

A wafer 70 or other substrate is supported on a pedestal 72 configuredas an electrode in opposition to the target assembly 18. A clamp ring 74maybe used to hold the wafer 70 to the pedestal 72 or to protect thepedestal periphery. However, many modern reactors use electrostaticchucks to hold the wafer 70 against the pedestal 72. An electricallygrounded shield 76 supported on the adapter 20 protects the chamberwalls and sides of the pedestal 72 from sputter deposition and also actsas an anode in the plasma discharge. The working gas enters the mainprocessing area through a gap 78 between the clamp ring 74 or pedestal72 and the shield 76. Other shield configurations may include anelectrically floating secondary shield inside the primary shield 76 andperforations through portions of the primary shield 76 protected by thesecondary shield to promote gas flow into the processing area.

A DC power supply 80 negatively biases the target assembly 18 withrespect to the grounded shield 76 and causes the argon working gas to beexcited and discharge into a plasma. The magnetron 42 concentrates theplasma and creates a high density plasma (HDP) region 82 underneath themagnetron 42 inside the main chamber 12. The positively charged argonions are attracted to the target assembly 18 with sufficient energy tosputter the metal from the target assembly 18. The sputtered metaldeposits on and coats the surface of the wafer 70. Preferably forsputter depositing into deep and narrow holes, an RF power supply 84 isconnected to the pedestal electrode 72 through a capacitive couplingcircuit 86, which acts as a high-pass filter, to create a negative DCself bias on the wafer 70 with respect to the plasma. The self bias iseffective at accelerating positive metal ions or possibly argon ionstoward the wafer 70 in perpendicular trajectories that more easily enterhigh-aspect holes. The self bias also imparts a high energy to the ions,which may be controlled to differentiate sputter deposition on the wafer70 and sputter etching of the wafer 70. A computer-based systemcontroller 88 controls the vacuum pump 60, the argon mass flowcontroller 66, the power supplies 80, 84 and the drive circuits for themagnetron motors 32, 36 according to the desired sputtering conditionsand scan patterns input to the system controller 88 through a recordablemedium such as a CDROM inserted into it or equivalent communicationlines.

A more realistic version of the epicyclic scan actuator 26 and attachedmagnetron 42 is incorporated into a illustrated in the orthographic viewof FIG. 2 in what is referred to as a universal magnetron mechanism(UMM) 100. The UMM 100 is supported on a flange 102, which is supportedon and sealed to a top wall of the cooling reservoir. A derrick 104supported on the flange 102 outside of the reservoir supports a verticalactuator 106 which can vertically move a slider which rotatably supportsthe rotary shafts 28, 30 and the motors 32, 36 coupled to them throughribbed belts 108, 110.

A sectioned side view of FIG. 3 illustrates a cooling reservoir 114formed in back of the target assembly 18 by a reservoir sidewall 116 anda reservoir top wall 118 on which the actuator flange 102 is supported.A water-sealed gearbox 120 and its counterweight 122 are fixed to thelower end of the outer rotary shaft 30 inside the reservoir 114. A sungear 124 is fixed to the lower end of inner rotary shaft 28 inside ofthe case 120 but is also captured between two sets of bearings. Afollower gear 126 is rotatably supported between another two sets ofbearings inside the gearbox 120 and is coupled through an unillustratedidler gear to the sun gear 124. A shaft 128 of the follower gear 126passes through a rotary seal on the bottom of the gearbox 120 and isfixed to a magnet arm 130 such that the magnet arm 130 is rotated by thefollower gear 126. The magnetron 42 and its counterweight 132 are fixedto opposed ends of the magnet arm 130. The gearbox 120 acts as an innerarm and the magnet arm 130 acts as the outer arm which in conjunctionwith the sun and follower gears 124, 126 act as a planetary gearmechanism.

The two separately controlled rotary shafts 28, 30 allow the magnetron42 to be scanned in a nearly arbitrary pattern. However, this widecontrol requires that the two motors 32, 36 be closely controlledtogether. That is, for many more complicated scan patterns, the rotationof one motor must be closely synchronized with that of the other motor.If the timing of the rotary shafts 28, 30 begin to drift apart, forexample, if one of the ribbed belts 108, 110 slips, the scan patternrapidly degrades.

A further problem with the independent control of the two rotary shafts28, 30 is that their relative rotation phase needs to be established andmaintained. Following the Miller design, as illustrated in the plan viewof FIG. 4, the top reservoir wall 118 includes a central aperture 134around which the actuator flange 102 is sealed and passing the rotaryshafts 28, 30 into the reservoir 114. The top reservoir wall alsoincludes a first sensor aperture 136 offset from the central axis 14 fora gearbox sensor and a second aperture 138 at a different radius fromthe central axis 14 for a magnet arm sensor. In this design, the sensorapertures 136, 138 are located 15° apart at two different radii withrespect to the central axis 14. The sensors which are inserted into thesensor apertures 136, 138 enable a homing function to establish and thenmonitor the rotation state of the two planetary arms. The sensorsoptically sense reflectors 140, 142 mounted respectively on tops of thecounterweights 122 and 132, which are respectively angularly fixed withrespect to the gearbox 120 and magnet arm 130.

Once the two arms have been home, the timing or relative phase of theirrotations need to be maintained. In one embodiment for improving thesynchronism, a computer-based motion controller 150, shown in FIG. 1, isinterposed between the system controller 88 and the motors 32, 36driving the rotary shafts 28, 30. For example, a DeviceNet (Dnet)communication link 152 transfers commands from the system controller 88to the motion controller 150. The Dnet communication system is a wellknown industrial computerized control system demonstrating highreliability and ruggedness. The motion controller 150 in turn controlstwo motor drives 154, 156 over a communication link 158 such as the wellknown Mechatrolink. [PLEASE PROVIDE SOME DETAILS OF THE FORMAT OF THEMECHATROLINK FORMAT AND TIMING} In general, the motion controller 150sends different sets of motion control signals to the two motor drives154, 156 indicating the respectively required motion of the two motors32, 36. The motor drives 154, 156 respectively power the two motors 32,36 with the required phase between the rotations of the motors 32, 36.

The system controller 88 sequentially polls the various elements underits control by transmitting the current control setting to therespective element. The polling period is on the order of a second orsomewhat less, which is not satisfactory for direct Dnet control of thetwo motor drives 154, 156. Instead, the motion controller 150 receivesthe current Dnet control setting, interprets it, and accordinglyperforms rapid and nearly continuous control of the motor drives 154,156.

A motor control circuitry 160 is shown in more detail in the schematicdiagram of FIG. 5. The motion controller 150, which may be a YaskawaMP2300, is powered by a 24 VDC supply and communicates with the systemcontroller 58 over a Dnet communication link 152. Each of the motordrives 154, 156, which may be a respective Yaskawa SGDS-08A12A,communicates with the motion controller 150 over a Mechatrolinkcommunication link 158. Each of the motor drives 154, 156 is poweredfrom a 208 VAC supply required for the motors 32, 36 and also from a 24VDC supply needed for the sensors. The motor drive 154 for the magnetarm 130 drives the associated motor 32, which in this embodiment is aservo motor, over a drive line 162 and receives a feedback signal fromthe encoder of the servo motor 32 over a feedback line 164. The motor 32for the magnet arm 130 will be referred to in the software explanationas the M2 motor. The arm motor drive 154 also receives a detectionsignal from a sensor 166 over a detection line 168. The sensor 166 maybe an optical sensor, such as an Omron E3T-SR21, which both emits a beamof light and receives a reflected beam from the reflector 142 associatedwith the magnet arm 130 to establish a position of the magnet arm 130.Similarly, the motor drive 156 for the gearbox 120 drives the associatedmotor 36, also a servo motor, over a drive line 170 and receives afeedback signal from the encoder of the servo motor 36 over a feedbackline 172. The motor 36 for the gearbox 120 will be referred to as M1.The gearbox motor drive 156 also receives a reflected beam from a sensor174 such as the previously described optical sensor over a detectionline the reflector 140 associated with the gearbox 120 to establish anangular position of the gearbox 120.

One mode of controlling the scan paths through the control circuitry 160of FIG. 2 would be to instruct each of the motors 32, 36 to rotate atrespective rotation rates once the associated arms have been positionedwith the desired phase between them. For example, if the arm motor 32 isinstructed to be stationary while the gearbox motor 36 rotates at a setrotation rate, the resulting scan path is that of the previouslydescribed PMR scan system with a fixed sun gear. In another example, ifthe arm and gearbox motors 32, 36 are instructed to rotate at the samerate in the same direction, the magnetron traces a circular path aboutthe target center 14 with the radius determined by the initial phasebetween the two arms.

Both of these simple patterns could be easily achieved with the use ofthe intermediate motion controller 150. However, the relatively slowcycle time of the Dnet controller 58 creates difficulties with morecomplex scan patterns. For example, a scan pattern 170 illustrated inFIG. 6 includes a generally circular scan about the target center 14near the target periphery and two smaller, somewhat circular scansoffset from the center 14, all to be performed in a few seconds. Asimilar scan pattern is portrayed in the graph of FIG. 7 in which trace182 plots the angular position in degrees of the center of the magnetronas a function of time and trace 184 plots its radial position in unitsof 0.1 inch (2.54 mm). The angle trace 182 shows the points of aprofile. The radius trace 182, though illustrated as continuous,includes corresponding profile points. This complex scan pattern needscloser control than that afforded by the Dnet communication protocolwhen the rotation rate is in the typical range of 60rpm.

In one embodiment of the invention, the system controller 88periodically polls the motion controller 150 on a somewhat coarse timescale while the motion controller 150 much more tightly and quicklycontrols the motor drives 154, 156. The polling may include bothcommands to the motion controller 150 and interrogations of it todetermine status of the elements associated with it. An example of acommand format for a command sent from the system controller 88 to themotion controller 150 is presented in TABLE 1. The command consists of 8bytes each of 7 bits.

TABLE 1 Byte Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0 0 CommandTicket Command Code 1 Enable Hard Stop 2 Command Data 3 Command Data 4Command Data 5 Command Data 6 Spare 7 Spare

Two bits of the 0 byte present the command ticket. The command ticketaccommodates the difference between the relatively infrequent pollingbetween the system controller 88 and the much quicker and tightercontrol of the motor drives 154, 156 taking into account that thepolling includes the most recent command even if that command is alreadybeing executed. The command code may assume any of four values 00, 01,10, 11. The 00 command ticket is a NOP, that is, to be ignored. Both thesystem controller 88 and the motion controller 150 keep track of thesequence of commands which have recently been sent. The systemcontroller 88 in each polling period sends a command. If the command isthe same as in the last polling period, the command ticket remains thesame. If the command changes from the last polling period, the systemcontroller 88 changes the command ticket to a new value among the threeactive values 01, 10, 11. The command ticket values do not necessarilyhave to cycle regularly through the three allowed values. That is, acommand ticket of 01 or 11 following a previous command ticket of 11will be interpreted as a new command ticket to be processed. On theother end, when the motion controller 150 receives a command with acommand ticket of the same value as the last receive command ticket, itis basically ignored since the command has already been processed.

The 6-bit COMMAND CODE instructs the motion controller 150 to performone of many operations, several of which will be described later.

An active ENABLE bit turns on both the M1 and M2 servo drives. TheENABLE bit should be turned inactive whenever drive engagement isundesirable, such as when changing parts or when a hardware interlockindicates an operational problem. An active HARD STOP bit acts an EMO,that is, stop operation as quickly as possible. The motors are stoppedat their maximum deceleration. The HARD STOP overrides the ENABLE.

The command contains 4 bytes of command data, the format of whichdepends upon the command. There are 2 bytes of spare formatting in thecommand protocol awaiting further development of the protocol.

An initial and exemplary set of command codes are present in TABLE 2.Although the command code is defined by six bits, the tabulated 16command codes are numbered in hexadecimal and require only four bits.

TABLE 2 COM CODE DEFINITION 0 NOP 1 HOME 2 ROTATE 3 STOP 4 MOVE M2 5PROFILE 6 CONFIRM HOME 7 SPIN M2 8 STOP SPIN M2 9 MOVE M1 A CLEAR ALARMB SET ROTATION ACCEL C SET MOVE M2 ACCEL D SET MOVE M2 SPEED E SET SPINM2 ACCEL F GET

A “0” command code indicates a NOP, that is, to be ignored.

A “1” command code indicates a HOME command to establish initialconditions for the angular positions of both the motors 32, 36 and henceof the magnet arm and the gearbox with the use of the sensors 166, 174and their associated reflectors 142, 140. This command may be issuedprior to continued production operation. An illustrative example of thehoming procedure is illustrated at the 3 o'clock position in theschematic plan view of FIG. 8, in which an inner arm 190 rotates aboutthe central axis 14 of the target assembly 18 and an outer arm 192rotates about a pivot axis 194 near the distal end of the inner arm 190and supporting an unillustrated magnetron near the distal end of theouter arm 172. The inner arm 190 corresponds to the gearbox 120, theouter arm 192 corresponds to the magnet plate 130, and the pivot axis194 corresponds to the axis of the shaft of the follower gear 126. Thesensors 166, 174 are positioned over the rotatable arms 190, 192. Theobject is to position the arms 190, 192 under their respective sensors174, 166 to initialize their positions. The figure assumes that the homeposition in the one in which the arms 190, 192 in their home positionsare parallel with maximal extent of the outer arm 192 and does notinclude the complexity of the planetary gear mechanism of FIGS. 2-4 thatthe sensors 166, 174 are not arranged along a single radius and that thereflectors 140, 142 associated with the arms 190, 192 may be located atdifferent angular positions, for example, on the counterweights oppositethe arms 170, 172 across the central axis 14.

The homing procedure first begins with the motion controller 150instructing the gearbox motor 36 to rotate the inner arm 190 until theinner sensor 174 indicates its underlying position. The sensor detectionmay be slow so that it is necessary for the procedure to hunt for theinner home position by subsequent back and forth movement of the innerarm 190 across the position of the inner sensor 174 until an inner homeposition is established. Then, with the inner arm parked in its homeposition, the motion controller instructs the arm motor 32 to rotate theouter arm 192 until the outer sensor 166 indicates its underlyingposition. Again, hunting for the outer home position may be required.The result is the illustrated home positions of the two arms 190, 192from which all subsequent movement is referenced.

A “2” command code indicates a ROTATE command, which instructs the twomotors 32, 36 to rotate at the same rate in the same direction. For aplanetary gear system, equal rotation means that the two arms 190, 192rotate in parallel so that, as illustrated in the 12 o'clock position inFIG. 8, the two arms 190, 192 remain aligned. If the ROTATE command isissued while the arms 190, 192 are out of phase, that is, not aligned,the subsequent synchronous rotation maintains the phase between the arms190, 192 during subsequent rotation.

A “3” command code indicates a STOP command, which stops the rotationsof the motors 32, 36 is they are indeed in motion.

A “4” command code indicates a MOVE M2 command, which causes the motor32 to move the outer arm 130 to a phase angle, specified in the datafield of the command, relative to the angular position of the gearbox120. For example, if a MOVE M2 command were issued after the arms hadbeen positioned in the 12 o'clock position of FIG. 7 such that the outerarm 182 would move in a retrograde motion to a new angular positionrelative to the inner arm 190, a resultant positioning is shown in the 9o'clock position in which the outer arm 192 is now perpendicular to theinner arm 190 with its distally supported magnetron well inside theperiphery of the target assembly 18.

A “5” command codes indicates a PROFILE command, which greatlyfacilitates the control of complex scan patterns with a relatively slowsystem controller 88. The scan pattern 170 of FIG. 6 can be decomposedinto a number of sections 190 connected between adjacent profile points192. The PROFILE command in essence allows the motion controller 150 toconsult a locally stored profile pattern based on the profile points 192to instruct the motors 32, 36 to cause the magnetron to be scanned alongthe desired profile 170.

Multiple profiles may be pre-loaded in the motion controller 150. Twobytes of command data in the data command may be used to select which ofthe stored profiles is to be used. Two more bytes of command data may beused to indicate a profile factor, which represents the total run timeof the profile, for example, in millisecond.

The profiles may be stored in various forms. However, one convenientformat illustrated in TABLE 3 for a scan pattern similar to that ofFIGS. 6 and 7 includes a series of paired values of time, for example,enumerated in seconds, and a phase angle of the outer arm 182 relativeto the inner arm 190. Other scan patterns are also stored in the motioncontroller 150.

TABLE 3 401 0 0 0 0.0025 0 0.005 0 0.0075 0 0.01 0 . . . 0.13 0 0.132520 0.135 78 0.1375 176 . . . 0.995 360000 0.9975 360000 1. 360000

The first entry in the table indicates the number of position data tofollow in the table. In the remainder of the table, the first columnindicates a time in second, for example, with a constant time differencein 25ms between the entries, and a phase angle between the outer arm andthe inner arm, for example, in units of milli-degrees. The indicatedpattern controls the magnetron to first scan in a generally circularpattern near the periphery of the target before changing to a morecomplex pattern, which ends up with another outer circular scan.

The motion controller 150 normalizes the 1-sec period of the storedtrajectory according to the profile factor included in the data field ofthe PROFILE command. The rotation rate of the inner arm 190, to whichthe rotation of the outer arm 182 is referenced by the PROFILE command,may be set by a preceding ROTATE command. The motion controller 150 mayperform a calculation from the profile table to determine at what ratethe motor for the outer 5 arm 182 needs to rotate to move the magnetronfrom the previous position in the profile table to the next position.[???] The rotation rate set by the ROTATE command determines the lengthof time for the scan pattern set by the PROFILE command. [???] Morecomplicated paths between two or more neighboring points on the selectedprofile may be calculated. Significantly different multiples profilesmay bepre-loaded into the motion controller 150 to be selected by thesystem controller 88.

One process for scanning a magnetron in accordance with a stored profileis illustrated in the flow diagram of FIG. 9. In step 200, the HOMEcommand causes both motors and their associated arms to home to theirhome positions. It is not necessary that the home positions correspondto maximal extent of the arms, only that their positions be known. Instep 202, the ROTATE command causes both motors and hence their arms inthe case of a planetary gear mechanism to rotate at a same rate, forexample, 60 Hz, thus producing a circular scan of the magnetron aboutthe central axis. In step 204, the MOVE M2 command instructs the outerarm to move the magnetron to a position facilitating ignition of theplasma, for example, near the chamber wall at the target periphery. Oncethe plasma has been ignited, in step 206, a MOVE M2 command instructsthe outer arm to move to an initial position. In step 208, a PROFILEcommand instructs the movement of the magnetron according to adesignated scan path for a designated length of time. At the completionof the PROFILE step 208, the plasma is extinguished and control returnsto the ROTATE step 202. During this period, the wafer processedaccording to the profile is removed from the chamber and replaced by afresh wafer.

It is desirable that the scan pattern, for example, of FIG. 6 or 7 betriggered by the PROFILE command and not be referenced to a set angularposition on the target assembly 18. The traces 182, 184 of FIG. 7 can bereferenced to an initial angular position at time equal to zero andchange from the actual angular occurring at that time. Typically,azimuthal angle during processing of a wafer is not important as long asproper averaging is achieved, but it is desired that the targetsputtering be azimuthally averaged to prevent local over sputtering, forexample, between the areas of the illustrated tracks if they wererepeated for each wafer.

A “6” command code indicates a CONFIRM HOME command, which is somewhatsimilar to a HOME command but is performed on the fly, that is, whilethe arms are rotating at operational rates to determine thatsynchronization has not been lost between the motors because of beltslippage or other reasons. The operation on the fly is quicker than thehome operation and also indicates if there is a problem with loss of theoriginal homing position.

The operation of the CONFIRM HOME command assumes that the motors andarms are synchronously rotating according to the ROTATE command. The M2motor 32 is instructed to move the magnet arm 130 to a position when itsreflector 142 should pass under the associated sensor 166. The gearboxsensor 174 should be triggered once per revolution with a few degrees ofthe rotary position based on the previous homing operation. If not, analarm is flagged issued and trouble shooting is required. The magnet armsensor 166 should similarly be triggered once every revolution. If not,an alarm is flagged and a HOME command is issued to rehome the motordrives 154, 156. [WHY DOES GEARBOX LOSS OF HOMING REQUIRE MAINTENANCEWHILE MAGNET ARM LOSS REQUIRES ONLY REHOMING??]. If homing is confirmedfor two consecutive rotations, the magnet arm 130 is returned to itsoriginal position and rotation continues until instructed otherwise.

A “7” command code indicates a SPIN M2 command, which allows the magnetarm 130 to rotate at a different rate and even direction than thegearbox 120, that is, to rotate asynchronously. Its four bytes of dataspecify the speed of the M2 motor 32 for the magnet arm 130. The speeddata is signed and a negative value indicates reverse or retrograderotation relative to the gearbox 120.

An “8” command code indicates a STOP SPIN M2 command, which stops theasynchronous spinning of magnet arm 130 resulting from the SPIN M2command. Instead, the M2 motor 32 is instructed to rotate or at leastplace the magnet arm 13 in synchronism with the gearbox 120, that is,according to the any previously issued ROTATE command [???]. The phasebetween the two motions is indicated by the angle data included in theSTOP SPIN M2 command.

A “9” command code indicates a MOVE Ml command, which instructs the M1motor 36 to rotate or move the gearbox to a position indicated by thedata of the MOVE M1 command. This is a static operation. The state ofthe other, M2 motor 36 does not matter.

An “A” command code indicates a CLEAR ALARM code, which instructs themotion controller 150 to clear any previously issued alarm flags andreturn to normal operation.

Command codes “B” indicates SET ROTATION ACCEL, which sets the ROTATIONacceleration for both motors according its included data. This commandshould be sent before any ROTATION command is sent and remains in forcethereafter [???].

“B” and “C” command codes indicate respectively a SET MOVE M2 ACCELcommand and a SET MOVE M2 command, which set the acceleration and speedapplied in the MOVE M2 command in moving the magnet arm 130 to aposition specified in the latter command.

Similarly, a E″ command code indicates a SET SPIN M2, which sets theacceleration used in the SPIN M2 command in instruct the asynchronousspin rate of the magnet arm 130.

An “F” command code indicates a GET command, in which the systemcontroller 88 interrogates the motion controller 150 for the value of apiece of data specified in the data field of the GET command. The datamay be identification of the motion controller 150, alarm state, or acurrent value of control parameter being imposed on the motors.

Even though the motion controller 150 allows complex scanning patternsand rapid control of the servo motors, it also allows conventionalscanning to be performed in which the servo motors are instructed torotate at specified speeds for relatively long periods of time whichcould be handled by system controller 88 alone.

The Dnet communication link 152 is bidirectional so that the motioncontroller 150 not only receives instructions but also sends responsesto the system controller 88. A response may be automatically returnedafter a command has been received to inform the system controller 88that the commanded action has been completed or perhaps that it failedand accompanying data may confirm the desired operational parameters.The CONFIRM HOME command in particular is expecting a response. Aresponse may include an alarm fault flag. The response may follow a GETcommand in which requested data are returned to the system controller88.

A response format is similar to the command format of TABLE 1 but may belonger in some response types to accommodate two or more pieces of datasent to the system controller 88. The response advantageously includesthe previously described command ticket [IS THIS JUST THE COMMAND TICKETWHICH WAS SENT TO THE MOTION CONTROLLER OR A SEPARATE COMMAND TICKET FORRESPONSES?]

The invention may be applied to other types of scanning mechanismsrequiring two or more motors to be separately controlled to effect anearly arbitrary scanning pattern, particularly if the motors need to beasynchronously operated. The motors may be of types other than servomotors. The communication links are not limited to the types described,but the invention provides significant advantages when the communicationlink to the motors operates significantly faster than the link to thehost controller.

[NEED SOME DESCRIPTION OF CONTROL OF SERVO MOTORS]

The invention thus allows the magnetron to be scanned in complexpatterns without a significant upgrade or even modification of thesystem controller. The invention also provides an efficient procedurefor confirming the homing condition of the motor magnetron withoutimpacting the throughput of the system.

1. A control mechanism for controlling the movement of a magnetron in asputtering chamber having a scanning mechanism for allowing azimuthaland radial movement of the magnetron about a central axis, comprising:two motors mechanically coupled to the scanning mechanism; and a motioncontroller connected over a polling communication link to a systemcontroller and receiving commands for a scanning path of the magnetronand separately controlling rotational speeds of the two motors androtational phase therebetween.
 2. The control mechanism of claim 1,further comprising two drive circuits connected between the motioncontroller and respective ones of the motors.
 3. The control mechanismof claim 2, wherein the motors are servo motors and the drive circuitsreceive encoder signals from the respective motors.
 4. The controlmechanism of claim 1, wherein the motion controller includes a memoryrecorded with a plurality of scanning profiles for the scanning path;wherein a profile command sent from the system controller selects ascanning profile; and wherein the motion controller controls therotation speed and rotational phase according to the selected scanningprofile.
 5. The control mechanism of claim 4, wherein the scanningprofile includes a plurality of pairs of time and said rotation phase.6. The control mechanism of claim 1, wherein the commands include acommand ticket and wherein the motion controller stores as first valueof the command ticket received in a first command and executes animmediately subsequent command only if a value of its command ticket isan acceptable value other than the first value.
 7. The control mechanismof claim 1, further comprising: a first arm rotatable about a centralaxis; a second arm rotatable about a pivot axis on the first arm offsetfrom the central axis and supporting the magnetron at a point offsetfrom the pivot axis; two sensors disposed respectively detecting thepresence of the two arms; wherein the commands include a dynamic homingcommand; and wherein the motion controller in response to the dynamichoming command processes signals from the two sensors while the arms arein motion to determine if the arms are at predetermined positions atpredetermined times.
 8. The control mechanism of claim 7, wherein thesensors are disposed at two different radii from the central axis. 9.The control mechanism of claim 8, wherein the sensors are opticalsensors, each emitting a beam of light and detecting light, and furthercomprising reflectors disposed on the first and second arms.
 10. Amethod of controlling a two-axis scanning mechanism for a magnetronrotating adjacent a target in a plasma sputter chamber, comprising thesteps of: periodically sending commands to a motion controller; andinterpreting those commands in the motion controller to send drivesignals to two motors coupled to the scanning mechanism to execute ascanning path of the magnetron adjacent the target.
 11. The method ofclaim 10, further comprising storing in the motion controller aplurality of scanning profiles, wherein one of the commands is a profilecommand selecting one of the scanning profiles and the motion controllersends the drive signal which causes the scanning mechanism to executethe scanning path corresponding to the selected scanning profile. 12.The method of claim 10, wherein each command includes a command tickethaving one of a plurality of operational values and wherein the motioncontroller interprets the command only if its command ticket has anoperational value different from that of an immediately previously sentcommand.
 13. The method of claim 10, wherein one of the commands is adynamic homing command and further comprising: upon sending of thedynamic homing command, the motion controller interrogates two sensorssensing positions of two portions of the scanning mechanism to determineif the portions are at preselected positions at preselected times. 14.The method of claim 13, wherein, if the portions are not at thepreselected positions at the preselected time, rehoming the scanmechanism.